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https://issues.apache.org/jira/browse/HADOOP-3149?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Owen O'Malley updated HADOOP-3149:
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Status: Open (was: Patch Available)
Alejandro,
Sorry it took so long to get back to this one! I'm still troubled about
having two classes in mapred.lib that do almost exactly the same thing. What
would be the changes to Runping's interface that would make you happy with it?
On a more pragmatic note, you don't need the InternalFileInputFormat. Just put
it into the MultipleOutputs.
It also bothered me to see you getting the default file system, but it is fine
because you are just feeding it to the output format that shouldn't be using
the file system parameter anyways.
> supporting multiple outputs for M/R jobs
> ----------------------------------------
>
> Key: HADOOP-3149
> URL: https://issues.apache.org/jira/browse/HADOOP-3149
> Project: Hadoop Core
> Issue Type: New Feature
> Components: mapred
> Environment: all
> Reporter: Alejandro Abdelnur
> Assignee: Alejandro Abdelnur
> Fix For: 0.18.0
>
> Attachments: patch3149.txt, patch3149.txt, patch3149.txt,
> patch3149.txt, patch3149.txt, patch3149.txt, patch3149.txt, patch3149.txt,
> patch3149.txt, patch3149.txt
>
>
> The outputcollector supports writing data to a single output, the 'part'
> files in the output path.
> We found quite common that our M/R jobs have to write data to different
> output. For example when classifying data as NEW, UPDATE, DELETE, NO-CHANGE
> to later do different processing on it.
> Handling the initialization of additional outputs from within the M/R code
> complicates the code and is counter intuitive with the notion of job
> configuration.
> It would be desirable to:
> # Configure the additional outputs in the jobconf, potentially specifying
> different outputformats, key and value classes for each one.
> # Write to the additional outputs in a similar way as data is written to the
> outputcollector.
> # Support the speculative execution semantics for the output files, only
> visible in the final output for promoted tasks.
> To support multiple outputs the following classes would be added to
> mapred/lib:
> * {{MOJobConf}} : extends {{JobConf}} adding methods to define named outputs
> (name, outputformat, key class, value class)
> * {{MOOutputCollector}} : extends {{OutputCollector}} adding a
> {{collect(String outputName, WritableComparable key, Writable value)}} method.
> * {{MOMapper}} and {{MOReducer}}: implement {{Mapper}} and {{Reducer}} adding
> a new {{configure}}, {{map}} and {{reduce}} signature that take the
> corresponding {{MO}} classes and performs the proper initialization.
> The data flow behavior would be: key/values written to the default (unnamed)
> output (using the original OutputCollector {{collect}} signature) take part
> of the shuffle/sort/reduce processing phases. key/values written to a named
> output from within a map don't.
> The named output files would be named using the task type and task ID to
> avoid collision among tasks (i.e. 'new-m-00002' and 'new-r-00001').
> Together with the setInputPathFilter feature introduced by HADOOP-2055 it
> would become very easy to chain jobs working on particular named outputs
> within a single directory.
> We are using heavily this pattern and it greatly simplified our M/R code as
> well as chaining different M/R.
> We wanted to contribute this back to Hadoop as we think is a generic feature
> many could benefit from.
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